An image forming apparatus is known which fixes a toner on a sheet. In some cases, the image forming apparatus forms images on two sides of a sheet (double-side printing). At this time, the image forming apparatus forms a first toner image to be transferred on the surface of the sheet. After transferring the first toner image onto the surface of the sheet, the image forming apparatus fixes the first toner image on the surface of the sheet using a fixer. The sheet on which the first toner image is fixed is reversed by a reverser. Then, the image forming apparatus forms a second toner image to be transferred on the back of the sheet. The image forming apparatus receives the sheet fed from the reverser. After transferring the second toner image onto the back of the sheet, the image forming apparatus fixes the second toner image on the back of the sheet using the fixer.
The fixer is equipped with a heat roller and a press roller which heats and presses the toner images while clamping the sheet therebetween.
In double-side printing, the image forming apparatus separately carries out an image formation operation and an image fixation operation twice for a sheet. Thus, double-side printing process is twice as long as single-side printing. Further, the press roller needs to be preheated by the heat roller before the fixer fixes the toner image on a side. Thus, the fixer consumes double power in the double-side printing when compared with that in single-side printing.
Thus, double-side printing, when compared with single-side printing, increases both print time and power consumption.